Regulation of Gene Expression in Prokaryotes And Eukaryotes - IJPR

International Journal of Pharmacy Research 0976-2167

Vol. 10, No. 1, 2019

Regulation of Gene Expression in Prokaryotes And Eukaryotes

Sapna Verma1*, Ashish Kumar2, Asheesh Kumar Gupta3

Review Article

1*Department of Biotechnology, UCALS, Uttaranchal University, Dehradun, India 2. NET Pharmacy College, Raichur, Karnataka, India 3.Uttaranchal Institute of Pharmaceutical Sciences, Uttaranchal University, Dehradun, India

ABSTRACT

The mechanism which stimulates the expression of certain genes and inhibits that of other is called regulation of gene expression. It is possible only if the organism has a mechanism of regulating gene activity by allowing some to function and others to restrain their activity through switching on and switching off system. This means, the genes are turned on or off as per requirement. A set of genes is switched on when enzymes are required to metabolise a new substrate. The enzymes produced by these genes metabolise the substrate. The molecules of metabolite that come to switch on of the genes are termed as inducers and the phenomenon is called induction. Certain genes continue to express themselves till the end product of inhibits or repress their expression. Inhibition by an end product is known as feedback repression. In eukaryotes the gene expression could be expressed at transcriptional level, processing level, translocation of mRNA and translational level.

Key words: Gene expression, Regulation, Acetylation, Phosphorylation, Methylation

Corresponding Author*: Sapna Verma, Research Scholar, Department of Biotechnology,

UCALS, Uttaranchal University, Dehradun, India, 248007

Email: sapnavrma06@

Article Info: Date received: 8 Jan. 2019

Date accepted: 22 Mar. 2019

INTRODUCTION

Gene expression is the process by which nucleotide the genetic code of a gene is utilised for protein synthesis and cell structure production. Transcription and translation the two main steps involve in

expression. The on?off of transcription process is the main regulatory control of the gene expression in prokaryotes whereas, more complex regulatory mechanism of transcription takes place in eukaryotes[10].

The process of gene expression- RNA synthesis steps is taken place in transcription process[1]. Translation process involve in formation of amino acid sequences. After gene expression, gene regulation is also needed for controlling rate and manner of gene

Gene regulation mechanism include the: regulation of rate of transcription, processing of RNA molecule, regulate the stability of mRNA molecules, regulating the rate of translation. Post- transcriptional and posttranslational regulation mechanism also

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applied after complete synthesized of gene. There are four identifiable steps during transcription: promoter recognition, chain initiation, chain elongation, chain termination. Promoter plays a vital role in the initiation of transcription of a particular gene.[11] to the promoter sequence RNA polymerase binds, which performs the transcription process, and then beings to work, constructing RNA to match the DNA nucleotides over which the enzyme passes. Inhibitor has also an essential role to prevent the expression of a certain gene. Inhibitors is often used in research either transcription or translation process. During gene expression regulation process occur in two pathways: positive and negative regulation. In human DNA exist in methylated form. Loss of transcriptional activity occur in methylation and inactivation of gene occur. DNA demethylation is also occur along with methylation in which gene promoter is linked to transcriptional activation and gene expression[24]. Histone acetylation and deacetylation, phosphorylation, Dephosphorylation is the further essential steps for gene expression regulation.

Proteins are coded by thousand of gene in cell, it is not necessary that every gene actively producing proteins at all the time. In this process we will study some of the factors which may regulate the gene expression and gene regulation, whenever the gene is in active state. To be expression gene, gene are transcribed into mRNA to protein and the protein become functional. Gene expression occur at any step under the following process[1].

Transcriptional control: some of the factors are regulating the transcription

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process. Transcription is the first step for gene expression, in which formation of a gene which is used to form a product, known as a protein. In transcription here the synthesis of RNA molecules from the single stranded DNA.[3] transcription is most important and selective process in the organism [Prokaryotic and Eukaryotic].

Post transcription: it is the biological process, that occur newly transcribed primary RNA [hnRNA], this step occurs prior to the translation of the protein. In capping nacent mRNA involves the addition of the 7 methyl guanosine at the end. In tailing cleavage of the 3 end and then the addition around 250 adenine residues to form a poly A tail also known as a polyadenylation[1].

TRANSLATION

Translation is the universal process in the both eukaryotes and prokaryotes. Translation where protein is synthesis in the cell and it is the second step of genetic expression. Decoding involves in the translation a messenger RNA and using information to build chain of amino acid and polypeptide. In the translation the codons of messenger RNA are read of DNA direction from 5' to 3'by molecules called transfer RNAs[4]. Translation done in three step: in the process of initiation the ribosome is together with target mRNA. The first tRNA will attached at a start codons. In the elongation, amino acid are brought to the ribosome by the tRNAs and linked together to form a chain. Termination is the last stage of translation, the achieved polypeptide is released to go and do its work on the cell[8].

How is gene expression regulated?

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Vol. 10, No. 1, 2019

The amount of gene of molecules in a cell describe the function of the cell. The control point for the gene expression is usually at the initiation of transcription. Some of the gene expressed as a part of the cell differentiation process and some are expressed at result of cell differentiation process. Eukaryotes transcription somehow complex the prokaryotic transcription because in the eukaryotic transcription the intervening sequence that are not a part of the mature RNA called introns are removed and are spliced together with the proteins coding region called exons, by the process called splicing.[1]

GENE REGULATION

In Eukaryotes

There are intracellular organelles in

eukaryotic cells which result to complexity. In

nucleus DNA is to be founded in eukaryotic

cells. Transcription process occurs in nucleus

and transcribed into RNA. Newly synthesized

RNA transported into cytoplasm, where

translation of RNA into protein occur by

ribosomes. Transcription and translation

process are physically separated by the

nuclear membrane, within the nucleus

transcription and outside the nucleus in the

cytoplasm occur. Regulation of gene

expression can occur at: epigenetic,

transcriptional,

post-transcriptional,

translational and post-translationaal[9].

Transcription, translation and RNA processing (post transcriptional changes) stage is the regulation stage of gene expression. The on?off of transcription process is the main regulatory control of the gene expression in prokaryotes whereas, more complex regulatory mechanism of transcription takes place in eukaryotes.[10]

In Prokaryotes

In cell cytoplasm DNA of prokaryotic organisms floats freely because of singe celled organisms that lack a cell nucleus. Process of transcription and translation occur simultaneously. Transcription stops when resulting protein is no longer needed. Controlling of types and quantity of protein is expressed in a prokaryotic cell is the regulation of DNA transcription. More transcription process occurs when more protein is needed. Therefore control of gene expression at the transcriptional level occur in prokaryotic cells.

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Spatial regulation of Tubulin genes in plant

Tubulin polypeptides is considered as building blocks of microtubules. There are two types of tubulin polypeptides and , one molecule of each type form a diamer. These dimmers then assemble in parallel rows to form a hollow cylindrical microtubules. These microtubules aggregets to form complex structure like cilia and flagella. In the cytoplasm and below the plasma membrane around the nuclear membrane. In cell movement these microtubules play important role and responsible for moving chromosomes during mitosis[10].

Temporal regulation of globin genes in animal

In eukaryotes and globin is a polyeptides that forms a pocket to bind with oxygen molecules. Gene within each cluster are duplicate of ancestral globin gene, form a small multigene family. During Frame

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Vol. 10, No. 1, 2019

shifting and chain terminating mutation sometimes abolish the ability to make polypeptide. These noncoding genes are called pseudogenes ().one side cluster genes are expressed in embryo and middle side expressed in fetus and other side genes expressed only after birth. Globin and in Arabidopsis expressed in tissue specific manner. Other globin and in vertebrates are expressed in temporal pattern during development. .[10]

REGULATOR OF GENE EXPRESSION

Activator

Gene expression activator is a protein that increases the gene transcription of a genes or set of genes. To turn on gene expression, activator is required in eukaryotic cells. To stimulate the assembly and activity of the transcription machinery at gene promoters activators bound to enhancers. To make the control of gene expression easier genes are organized. Immediately upstream of the coding sequence the promoter region is found. Promoter is as longer, the more available space for proteins to bind. This also do more control to the transcription process. The length of the promoter is gene-specific and can differ between genes. The level of control of gene expression can also differ quite dramatically between genes. The promoter is bonded transcription factors that control the initiation of transcription[11].

Just upstream of the transcriptional start site, resides the TATA box Within the promoter region,. This box is a repeat of thymine and adenine dinucleotides. RNA polymerase binds to the transcription initiation

complex, allowing transcription to occur. To initiate transcription, a transcription factor (TFIID) is the first to bind to the TATA box. Binding of TFIID recruits other transcription factors, including TFIIB, TFIIE, TFIIF, and TFIIH to the TATA box. RNA polymerase can bind to its upstream sequence Once this transcription initiation complex is assembled. RNA polymerase is phosphorylated ,When bound along with the transcription factors. Result of that of the protein from the DNA to activate the transcription initiation complex and places RNA polymerase in the correct orientation to begin transcription; DNAbending protein brings the enhancer, which can be quite a distance from the gene, in contact with transcription factors and mediator proteins.

Fig. 1. The process of transcription There are some regions that help to increase or enhance transcription, which is known as enhancer. Upstream of a gene, within the coding region of the gene,

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Vol. 10, No. 1, 2019

downstream of a gene, or may be thousands of the effect of blocking protein production and

nucleotides away could be the location of it.

ultimately its function.

The shape of the DNA changes occur When a DNA-bending protein binds to an enhancer. Interaction between the Activators bound to the enhancers and the transcription factors bound to the promoter region and the RNA polymerase to occur due to this shape changes. DNA is usually depicted as a straight line in two dimensions, which is actually a three-dimensional object. Therefore, a nucleotide sequence thousands of nucleotides away can fold over and interact with a specific promoter[12].

Inhibitors

Inhibitor is the process factor of gene

expression in a cell to prevent the expression

of a certain gene. Inhibitors is often used in

research either transcription or translation

process. Ribozymes are catalytic molecules

used to inhibit gene expression. By

cleaving mRNA molecules, these molecules

work. Essentially silencing the genes that

produced them. A natural process that cells

use to turn down, or silence, the activity of

specific genes is RNA interference (rnai). By

an enzyme called Dicer the double-stranded

molecule is cut into small double-stranded

fragments. These small fragments, which

include small

interfering

Rnas

(sirna) and microrna

(mirna),

are

approximately 21?23 nucleotides in length.

The fragments integrate into a multi-subunit

protein called the RNA-induced silencing

complex, which contains Argonaut proteins

that are essential components of the Rnai

pathway.[13]Inhibition of translation step has

METHYLATION

Methylation of DNA: DNA methylation is an epigenetic mechanism that cell use to control gene expression, which occur by the addition of a methyl group [Ch3] to the DNA molecules. Addition of methyl group is controlled at different level of cell and several family of enzyme called DAN methlytransferase [dmts]. Three different dnmts are required for maintenance or establishment of DNA methylation process, [DNMT1, DNMT3a and DNMT3b]. DNMT1 is responsible for the maintenance of the DNA methylation patterns and DNMT3a and DNMT3b is seem to establishment of new de novo DNA methylation patterns. Activity of DNA segment can be change by the methylation without changing the sequence. 5methylcytosine is found in the human approximately 1.5 percent of genomic DNA. DNA structure can be modified by covalent attachment of methyl group-DNA methylation. In the DNA methylation process is the covalent addition of the methyl group at a 5-carbon of the cytosine base forming in 5methylcytocine [5-mc],also known as "fifth base" of DNA. DNA methylation is an important component for various cellular process, including embryonic development, X-chromosomes inactivation, genomic imprinting and preservation of chromosomes stability.[13] DNA methylation usually inhibit the transcription of eukaryotes gene and it is particularly abundant in plant and vertebrates. In vertebrates and plant , cpg island [DNA methylation site] occur near many promoter of gene. These cpg island are commonly 10000

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